1. Field of the Invention
The invention relates to an x-ray examination apparatus comprising an x-ray image sensor matrix for deriving an initial image signal from an x-ray image, a correction unit for deriving a corrected image signal from the initial image signal.
2. Description of Related Art
Such an x-ray examination apparatus is known from the European patent application EP 0 642 264.
The correction unit of the known x-ray examination apparatus counteracts disturbances in the initial image signal which are caused by delayed emission of charges from the x-ray image sensor matrix. Incident x-rays release electric charge carriers, i.e. photocharges, notably photoelectrons, in the x-ray image sensor matrix and these electric charges are detected. The signal levels of the initial image signal represent the detected charges. A part of the charge carriers can be trapped in a trap-state, be retained in such a trap-state, and can escape from the trap-state at a later stage and are detected as electric charges with a delay. If the initial image signal with the disturbances were applied to a monitor for displaying the image information, not only the image information of the instantaneous image would be reproduced, but at the same time also image information of a previously picked-up image. As a result after-images would be displayed together with the instantaneous image.
The correction unit of the known x-ray examination apparatus utilises an intricate mathematical model based on physical considerations for the trapping and subsequent release of charge carriers so as to correct disturbances due to charge carriers emitted in a delayed fashion. A drawback of the correction unit of the known x-ray examination apparatus is that the computations required to obtain the corrected image signal are rather complicated so that a powerful arithmetic unit is required which nevertheless requires a rather long computation time. Hence, the time between forming the x-ray image and displaying the image information is relatively long so that the known x-ray examination apparatus is not well suitable for imaging rapid dynamic processes in which variations occur within a period of time comparable to the required computation time. Moreover, the required programming of the arithmetic unit is complicated, so that highly skilled staff is needed to set up the correction unit.